1. Field of the Invention:
The present invention relates to a copying machine and, more particularly, to a copying machine having a transparent plate on which an original to be copied is placed and an improved platen cover for overlying an original placed on the transparent plate.
2. Description of the Prior Art:
There have thus far been publicly known copying machines having the structures and functions shown, by way of example, in the sectional view of FIG. 1. Such machines include a photosensitive drum 1 having photoconductive material overlying the cylindrical surface thereof and, arranged in adjoining relation about the drum, a charge generating device 2, a toner developing device 3, an image transfer electrode 4, a separation electrode 5, a charge eliminating electrode 6 and a cleaning device 7 (moving along the direction of drum rotation--which is clockwise in the illustrated apparatus). Each sheet of recording paper 9 fed from magazine 8 passes between photosensitive drum 1 and image transfer electrode 4, during which a toner image on photosensitive drum 1 is transferred onto recording paper 9 and then ejected from the machine through a conveyance device 10 and a fixing device 11.
On the upper part of housing 12, a moving document glass plate 13 is moved at a limited speed in the direction of arrow "A" and carries a transparent plate 14 normally comprising a flat plane for receiving thereon an original D to be copied. A platen cover 15 serves to cover an original D placed atop transparent plate 14.
Directly under moving document glass plate 13, a light source 16 (such as a fluorescent lamp) illuminates original D through transparent plate 14. In addition, an optical exposure system comprising a mirror 17, a lens 18 and a mirror 19 is disposed between glass plate 13 and drum 1, through which optical system an image of an original D on transparent plate 14 is focussed onto the surface of photosensitive drum 1.
After photosensitive drum 1 is charged by charge generating device 2, an electrostatic latent image is formed on its photosensitive surface in accordance with the image of original D focussed onto the surface of rotating drum 1. This electrostatic latent image on the surface of drum 1 is then converted to a visible toner image thereof on passage through toner developing device 3.
In the copying machine just described, the optical exposure system is fixed while a document glass plate 13 is moved synchronously with the rotation of a photosensitive drum 1 to form an electrostatic latent image of an original D on the surface of the drum. Also publicly known are copying machines in which the document glass plate remains fixed on the machine housing and the optical exposure system is moved synchronously with the photosensitive drum to form an electrostatic latent image of an original D on the photosensitive drum.
In both these types of copying machines, a platen cover 15 is normally utilized to press the original D on transparent plate 14; if no platen cover is used, the following defects result:
(1) Shifts in the relative positions of an original and a recording sheet of the same size cause a black line to appear on the edge of the recording paper, degrading the quality of the resulting copy image. PA1 (2) When copying on a recording sheet of larger size than that of the original to be copied, a black frame appears around the image reproduced on the recording sheet with a corresponding degradation of copy image quality. PA1 (3) When the original to be copied is smaller than the size of the machine's capability for accepting original documents, an electrostatic latent image corresponding to the area of the difference of the sizes between them is formed on the circumference of the photosensitive drum 1; toner particles therefore adhere to that area of the latent image, whereby not only is toner wasted in large quantity, but the cleaning device is heavily loaded.
In order to remedy these defects, a platen cover is used to cover the original to be copied. Because the surface of the cover facing the transparent plate should have an optical reflection factor equivalent to or higher than that of a white surface (which is normally the background color of an original), however, it has thus far proved impossible to paint or print a letter, mark or pattern onto the surface of the platen cover that faces the transparent plate without degrading the quality of the resulting reproduction.